As for a process for chemically etching and removing an oxide film formed on a semiconductor wafer (hereinafter, simply referred to as “wafer”) as a substrate, there are known, e.g., a COR (Chemical Oxide Removal) process and a PHT (Post Heat Treatment) process. In the COR process, an oxide film formed on a surface of a wafer is made to react with hydrogen fluoride gas and ammonia gas, and ammonium hexafluorosilicate (AFS) is generated as a reaction by-product from the oxide film. In the PHT process, by heating the wafer, the generated AFS is removed by sublimation. In other words, the oxide film is removed by the COR process and the PHT process.
The COR process and the PHT process are performed in different process modules in consideration of improvement of a throughput. Therefore, a substrate processing system for removing an oxide film includes a transfer unit, e.g., a transfer arm, for transferring a wafer among the process modules. The transfer arm has a pick for mounting thereon the wafer. When the wafer is loaded into and unloaded from the process module, the pick of the transfer arm and a vicinity thereof move into the process module. Since sublimated AFS floats in a process module where the COR process is performed (hereinafter, referred to as “COR processing module”) or in a process module where the PHT process is performed (hereinafter, referred to as “PHT processing module”), when the pick of a low temperature (or a room temperature) moves into the corresponding process module, the sublimated AFS is solidified and adhered on the surface of the pick. The AFS adhered on the pick may be peeled off during movement of the transfer arm between the process modules and adhered as particles on the wafer. Accordingly, semiconductor devices manufactured from the corresponding wafer may have defects.
Therefore, conventionally, an operator opens a lid of the transfer module where the transfer arm is provided at a proper timing and performs wet cleaning on the transfer arm. In that case, the inside of the transfer module is exposed to the atmosphere. Since, however, the inside of the transfer module needs to be maintained in a vacuum state, time is required to restore the substrate processing system by decompression after the wet cleaning.
Therefore, there has been recently proposed a technique that prevents sublimated AFS from being solidified on the surface of the pick or the like even when the pick of the transfer arm and the vicinity thereof move into the COR processing module or the PHT processing module by providing a heating room in addition to the process module and heating the pick of the transfer arm and the vicinity thereof in advance in the heating room (see, e.g., Japanese Patent Application Publication No. H11-354503). Accordingly, AFS is prevented from being adhered to the pick or the like and, further, generation of particles can be suppressed.
However, in the method disclosed in Japanese Patent Application Publication No. H11-354503, a cost of the substrate processing system is increased because the heating room needs to be provided. In addition, even if the pick or the like is heated in the heating room, the pick or the like is cooled during movement to the process module. Therefore, in order to maintain the temperature of the pick or the like at a preset level or above, it is required to heat the pick or the like in advance in the heating room whenever the pick or the like moves into the COR processing module or the PHT processing module. As a result, the throughput is not improved. It may be considered to maintain the temperature of the pick or the like at the preset level or above for a certain period of time by excessively heating the pick or the like. In that case, however, excessive heat may be applied to components of the driving mechanism of the transfer arm and this may inflict thermal damage on the driving mechanism.